Underfloor heating with latent heat storage

Abstract

Underfloor heating is known for its comfort due to the low and favourable temperature gradient in the heated space above the large floor area available for heating. This paper addresses the idea of improving the existing underfloor heating system by using an encapsulated phase change material (PCM) that melts and solidifies at about 28 °C, placed in the concrete floor during construction. The objective is to minimize the fluctuation in the floor surface temperature and to have sufficient heat storage so that heating can be done during the off-peak electricity period only. Two concrete slabs (0.5 m × 0.5 m × 0.095 m) were constructed with a hot water pipe embedded in both of them to provide the required heating. Nodules having a diameter of 75 mm and containing CaCl₂6H₂O were placed in one of the concrete slabs prior to its moulding. Unlike the plain concrete slab, the concrete-PCM slab showed a much lower surface temperature fluctuation and maintained an acceptable surface temperature during the whole day even though the heating process was done for only 8 h. A simple one-dimensional model was developed to simulate the underfloor heating system, so that it can be used to optimize its design. Comparison between the measured and predicted performance of the two slabs for 3 days showed a reasonable agreement.